1. Field of the Invention
This invention relates to the art of cushions for wheelchairs, and more specifically to foam cushions for wheelchairs, and even more specifically to foam cushions designed to reduce pressure on the ischial tuberosities of the user and increase lateral pelvic stability.
2. Description of the Related Art
Users of wheelchairs are often unable to walk or stand. As such, they commonly spend long hours in a sitting position. Further, many of these users have no sense of feeling below their waist. They are unable to realize when portions of their body are being uncomfortably pinched between their bones and the supporting seat of the wheelchairs. If this situation goes undiscovered, painful and unhealthy sores can develop in the user's body under these bony prominences.
The primary bony prominence causing such difficulties are the ischial tuberosities of the user's pelvic structure. In the past, wheelchair cushion manufacturers have sought to address this problem by providing variously configured seat cushions to relieve the pressure on these ischial tuberosities. Some of the wheelchairs seat cushions have addressed this problem by the use of different density foams under the various portions of the user's buttocks and thigh region in an effort to support the user's weight and relieve the pressure on the ischial tuberosities.
One example of such a structure is disclosed in U.S. Pat. No. 3,987,507 to Hall wherein a pad assembly is made up of three pads of resilient foam material. A center pad has a greater density than the outer pads. The center pad also has three cut out openings at locations which correspond to the maximum pressure points exerted by a person sitting on the pads.
Another cushion utilizing foams of different densities is disclosed in U.S. Pat. No. 4,522,447 to Snyder et al. wherein the seat cushion comprises segments having different moduli of elasticity.
In U.S. Pat. No. 4,753,480 to Morell, a wheelchair cushion has a bottom pad of resilient foam material of high density and at least one upper pad of resilient foam material of intermediate density having a cut out therethrough. Filler foam material of low density is frictionally mounted as an insert in at least one of the openings of one of the upper pads.
In U.S. Pat. No. 4,819,288 to Lowthian, a foam wheelchair cushion features blocks and higher density foam in an intermediate layer than in an outer layer.
In U.S. Pat. No. 4,951,334 to Maier, a pressure relief cushion having a spring rate of about 75 to 300 pounds per inch features two different resilient materials, each having a different indentation force deflection rating and being substantially U-shaped.
While some of these prior art cushions have proven to be effective in some applications, improvements were desirable. Some of the designs were rather complex, requiring a high degree of precision in the assembly process as well as a corresponding higher cost. Further, some of the designs did not relieve pressure on the ischial tuberosities to the degree desired.
The present invention contemplates a new and improved wheelchair seat cushion which is simple in design, effective in use, and overcomes the foregoing difficulties and others while providing better and more advantageous overall results.